Sunderland players cannot hide their joy at beating Reading
O'Neill's side got the best possible start when James McClean fired in on the turn with just three minutes gone.
And they strengthened their grip on the game when Steven Fletcher back-heeled Danny Rose's cross in from eight yards, reports the BBC.
Sunderland's dominance continued and Stephane Sessegnon's finish added a fitting late flourish to their night.
Exactly a year ago, O'Neill oversaw a 2-1 home win over Blackburn in his first game as Sunderland boss - the first of seven victories in 10 games that convinced Black Cats fans they had found the ideal man to restore their flagging fortunes.
The general feeling at the Stadium of Light in the aftermath of this result - just a fifth win in 30 games - will be less one of unbridled optimism and more one of relief as their side claimed just a second home league win of the season to move up to 15th in the table.
However, the Sunderland support will also take heart from a performance that showcased the kind of desire and positivity their side have been lacking over a 10-month period that has left them little better off now in terms of league position than they were 365 days ago.